Stereo Hydrophone Technique

Question

I've got a stereo pair of JrF hydrophones which I've not used very much, other than just testing them out around the house. I'm planning a trip to the coast in a week or so and want to give them a further test by recording some sounds of the sea. The geography of the area is quite rocky, so there are lots of interesting rock pools etc which I anticipate may be good to record in. Pembrokeshire, to be precise.

Now the thing I'm trying to suss out is how best to do this. The water is of course tidal, and although I'm obviously not going to go near any spots with very powerful movements, there will still be some movement of the hydrophones in the water. To record in tight areas (where they may collide with the bank or bottom) and to get the most water movement over the hydrophones, should I anchor them in some way? I'm imagining something like a pole with two clamps on, holding them in a spaced omni type configuration. Does anybody do this? If it's a good idea, can I do it safely without damaging the JrF phones? I'm conscious of not wanting to damage the rubber sealant.

I understand that this will create a different type of recording to if they are free floating and that there is potential in that technique too. I've just not found much info on stereo techniques, but watching the video about the amazing ambient surround rig got me thinking about this.

Terrain:

Answer 1

I've done limited stereo recordings with the same hydrophones. I wish I had more of a solution for you but in short it sounds like you are on the right track for a successful operation.

I had trouble with the mics bumping into each other and into the bottom because I was recording in the surf. I ended up having to keep the two mics spread far enough apart so that they did not bump each other and in the middle of the water column so they were off the bottom. As you know they are very sensitive. The rubber casing seems very durable however.

Next time I do something like that again I'm thinking of constructing something similar to what you are describing and using beach fishing weights "spider weights" and attaching the mics to crabbing line. I haven't completed my method on this but basically looking to build a rig that can be dropped into water in the surf or off the side of a boat. Some sort of stereo bar may be needed to keep the separate and consistently spaced. Come to think of it a basic crab trap or basket may work for my uses as the bottom is typically pure sand where Im recording.

Answer 2

A bit of feedback for those interested - I didn't actually get as much time to put into this as I'd of liked, but did get a couple of interesting recordings:

Both of these were recorded in areas of quite powerful water movement, my idea of recording ambient sound from more tranquil pools didn't seem to work. I'm presuming this was because the hydrophones were not sensitive enough to pick these sounds up. I ended up attaching the hydrophones to an old stereo bar which worked quite well, better than using weights, though I understand this does work well for some.

Answer 3

here is my rig I built for my home build hydrophones. It has 3 levels of shock mount isolation. Sits well in surf and wave action. adjustable directional pivots. Very quiet. nes

My home made hydrophone with active preamp